1. Field of the Invention
The present invention relates to a crosslinkable composition crosslinkable by Real Michael Addition (RMA) reaction wherein a component with at least 2 activated unsaturated groups (hereafter also referred to as the RMA acceptor) and a component with at least 2 acidic protons C—H in activated methylene or methine groups (hereafter also referred to as the RMA donor) react and crosslink to each other in the presence of a strong base catalyst.
2. Description of the Related Art
RMA chemistry can be tuned to give very fast curing compositions (also at lower curing temperatures) in coating compositions at acceptable or good pot lives and good material properties, which makes this chemistry very attractive as a basis for coating compositions. Details of RMA cross-linkable compositions using a latent based cross-linking catalyst are described in application PCT/EP2011/055463 which is herewith incorporated by reference.
Real Michael addition is activated by strong bases, but also inhibited by the presence of acidic species that will consume these basic catalysts. In tuning the reactivity of coating systems in view of achieving a desirable drying profile, there are various requirements to balance. The drying profile (also referred to as the reaction profile or as the curing profile) is the progress of the cross-linking reaction as a function of time. It is required that the drying profile allows build-up of mechanical properties as fast as possible, to help the productivity of the coater. It is further also required to have a drying profile that is robust, i.e. the reactivity (and hence the resulting drying profile) is not strongly influenced by accidental low levels of acidic contaminants being present.
On the other hand it is required to have a good appearance of the resulting coating. This implies the need for sufficient levelling you are during the immediate period after application, when the curing coating composition is present as a liquid and capable of such levelling. This also implies the need for absence of artefacts like solvent inclusions or gas inclusions or other surface irregularities that may occur if curing is very fast, especially if it is faster at the surface than in deeper layers, which is often the case if curing occurs at the time scale of solvent evaporation or surface activation of a catalyst. Also film hardness build-up will be affected under conditions in which solvent entrapment occurs.
The described requirements are to some extent opposing each other. For a fast curing profile, but also for a high robustness against accidental acid contaminants high levels of catalyst are preferred, whereas at the same time such high levels of catalysts may negatively influence surface appearance and hardness development. The object of the invention is to provide an RMA cross-linkable composition that provides a better balance in these apparently counteracting requirements in particular in crosslinkable compositions having a high solid content.